The present invention relates generally to a pump construction, and more particularly to a pump construction which is particularly suitable for use in a reactor pump.
Reactor pumps are already well known and are therefore not believed to require specific detailed descriptions. It is necessary, however, to point out that these pumps are usually arranged so as to be vertically mounted in or on the pressure vessel. The pump wheels and a radial bearing of the shaft for the pump wheels are located within the pressure vessel and the drive motor, the shaft seal and an additional radial bearing for the pump shaft are located outside the pressure vessel. Such pumps, which are for instance used in boiling-water reactors, conventionally have a radial bearing for the pump shaft and which is located adjacent the pump wheel in the interior of the pressure vessel, the bearing being a hydrostatically operating bearing. A separate water supply arrangement for supplying water under pressure to the hydrostatic bearing is required.
In this particular field it is customary to use ferritic and austenitic materials for components serving to mount the pump within and without the reactor vessel, that is components which are located either within or without the vessel. Because of the differential coefficient of thermal expansion of these materials it has been observed that deformations of the pump mounting member occur, that is deformations transversely of the longitudinal axis of the member. In addition it has been observed that due to interior pressure acting upon these pump mounting members, they tend to move skew with reference to their intended position. The result of all this is the exertion of static forces on the bearing which must be absorbed by the bearings even while the pump is not in operation. Although for various reasons the use of hot water lubricated hydrodynamic radial bearings would be advantageous in such pumps, the above difficulties have thus far prevented the use of this type of bearings. Because the pumps are operated at differential speeds, the statically loaded hydrodynamic hot water lubricated radial bearings would be subjected to very significant wear at low operating speeds, and this is not acceptable.